1. Field of the Invention
The present invention relates generally to diagnostic equipment, and more particularly to apparatus for performing diagnostic tests on materials and/or structures to determine integrity of properties in low observable vehicles.
2. Description of Related Art
Typically, stealthy or xe2x80x9clow observablexe2x80x9d (L.O.) vehicles, and in particular, aerostructures, are provided with radar absorbing materials (RAM) in the form of structures or coatings having low radar visibility properties. They are also provided with radar reflective materials for controlling radar visibility properties, such as coatings on transparences, canopies, light lenses, optical sensor apertures, IR sensor apertures, conductive paints, conductive fillers, and conductive tapes. These L.O. materials historically experience failure, e.g. in the form of cracks, or damage, e.g. environmental effects such as wind, rain, hail, sun or thermal stresses. Additionally, such materials are known to be damaged through improper repair techniques.
In the use of such materials, it is desirable to be able to identify the location of such failures or damage so that repairs, replacement or covering of the failed or damaged locations can be effected with new materials or coatings. The identification and location of such failures has traditionally been achieved by specially trained engineers who use diagnostic equipment that require expert interpretation of the output. Against this background, the inventors have developed a diagnostic tool that will indicate with substantial precision the presence of failures in low observable (LO) structures and materials using a hand-held detection apparatus that quickly and easily indicates the status of LO integrity.
Existing art devices are limited in the scope of functions that they can perform and by environmental and ergonomic operational considerations. The present invention avoids these limitations by being multifunctional and applicable to environmental and ergonomic conditions that are beyond the capabilities of existing art devices.
Existing art devices traditionally are limited to use in a laboratory or manufacturing environment due to the safety issue of the explosive fuel environment that is found around operational aircraft. These devices use off the shelf equipment that contains high voltages and switches that are ignition sources. The present invention avoids this serious operational limitation by using sealed switches (power and function), sealed battery compartments and low voltages designed to allow the present invention to be operationally safe and efficient when used within explosive environments (fuel vapor) found around operational aircraft.
Additionally, such devices function is limited to identifying if the work piece is conductive, insulative or coated with radar absorbing material. The present invention avoids these limitations by additionally displaying the surface conductivity of the work piece and also by indicating whether the work piece is within specification, that is, whether the work piece is coated with radar absorbing material or not.
Existing devices use transmission line technology (waveguide, parallel plate, coaxial, or strip-line) or antenna technology to launch and receive RF or microwave energy to/from the item under test. The present invention avoids the limitations associated with such transmission technologies by using a two port RF or microwave structure that is made up of lumped and/or distributed inductance and capacitance (an RF or microwave circuit) as a sensor. This structure produces localized electric and magnetic fields that induce voltages and currents within the material under test. These voltages and currents within the material under test create electric and magnetic fields that are dependent on the electrical properties of the material under test. The fields thus produced by the material under test and sensor interact constructively and/or destructively thus altering the frequency, amplitude, and phase response of the sensor. Thus the properties of the material under test can be determined from the response of the sensor to the material under test. The configuration of the RF or microwave circuit is selected and optimized for the types of materials that are being tested.
Existing art devices are single function devices, whereas the present invention is multifunction. The maintainers of Low Observable (LO) vehicles require multifunctional tools to reduce operator training and simplify maintenance inspections. The desired functions are all performed by the present invention:
a) Conductive Materials
Surface resistance readout
Pass/Fail indicator
b) Absorptive Materials
Type of absorptive material
Material electrical properties
Backing type-conductive/nonconductive
Conductive Backing Quality (resistance readout)
Material thickness
Finally existing art devices can and often do produce repetitive motion injuries due to their weight and awkward hand positioning that is sometimes required during their normal use. Such motion injuries are caused by repetition, force and awkward reach (position). The present invention reduces force by reducing the weight of the portion of the device that is hand held. This is accomplished by separating the device into two portions. A lightweight sensor head that is connected to a belt pack unit with a lightweight cable. Awkward reach (position) is reduced through the use of bellows to self align the sensor with the surface under test and the ability to mount the sensor head on an extension pole reduces awkward position and reach.
It is therefore an object of the present invention to provide a novel intelligent, hand-held, diagnostic tool that will quickly and readily enable an inexperienced user to determine whether low observable properties in vehicle structures are present, absent, or substantially flawed, while overcoming many of the disadvantages and drawbacks of similar previously known diagnostic tools. Thus the present invention is capable of safe and efficient operation in potentially difficult/hazardous environments (explosive and/or toxic), such as fuel vapor areas, flight lines etc., found around operational aircraft.
Yet another object of the present invention is to provide a novel hand held, v diagnostic test device having a sensor unit with xe2x80x9cPassxe2x80x9d/xe2x80x9cFailxe2x80x9d indicator lights and a digital display located on the sensor head for indicating whether Radar Cross Section (RCS) performance has been degraded by damage, repairs or normal wear and tear, and a bellows on the sensor for insuring positioning of the sensor flush against the surface or structure of which the RCS properties are to be measured.
Still another object of the invention is to provide a novel diagnostic tool, which includes a sensor an/or sensors, xe2x80x9cintelligencexe2x80x9d electronics and software for determining the integrity of low observable properties in materials and structures of various vehicles, particularly aerostructures.